1. Field of the Invention
The present invention is related to wrapped wire electronic circuit boards and, more particularly, is directed toward a technique for verifying the wiring of such boards.
2. Description of the Prior Art
Wrapped wire electronic circuit boards are widely used in industry for mounting and interconnecting various electronic components. Typical wrapped wire electronic boards consist of a rigid substantially planar substrate which has a plurality of electrically conductive terminal pins or posts extending from one surface thereof. On the opposite surface of the board, means are provided for attaching various electronic components. The components are then electrically interconnected in a desired circuit configuration by hard-wiring the proper terminal posts or pins to one another.
Such wrapped wire electronic boards are preferred in place of conventional printed circuit boards in those instances where, for example, a prototype circuit is to be breadboarded, the production quantity of a particular circuit is relatively low, when wiring complexity is high and a double-sided printed circuit board is insufficient to accomplish the wiring objectives, when wiring changes are anticipated, and the like. For example, many computers utilize wrapped wire boards due to their flexibility and reliability.
Typical wrapped wire boards contain thousands of terminal posts or pins and have several hundreds of interconnecting wires. The wires may be connected between two terminals, or may be connected between a plurality of terminals, as the particular circuit configuration may dictate.
Wrapped wire boards may be wired either manually or with the assistance of a numerically controlled positioning machine. In such positioning machine, the board is mounted in a holder, and a paper tape controls the positioning of an X-Y indicator to point to successive terminals about which the wire is to be wrapped. The wire may then be manually or automatically wrapped about the indicated pin, and the machine will then step to the next pin in the sequence. The paper tape which controls the positioning machine is generated from a computer program which receives as input the coordinate pairs of pins which must be connected together. Typically, the program will act on the pairs of coordinates to generate a paper tape control which groups the wired pins into a plurality of branches, all of the pins within each branch being successively interconnected. In this manner, wiring of the board may be most efficiently effectuated.
After the board has been wired, it is necessary to inspect or test it in some manner for wiring accuracy. However, such inspections or tests are either extremely time-consuming or difficult to accomplish. One factor is simply the large total number of wires on the board, their high density placement, and the closeness of the pins to one another.
Those boards which are not checked for wiring accuracy, and which have components mounted thereon, run the risk of damaging the components, working improperly, and/or causing long delays to debug the circuit since it must be determined whether the malfunction is due to an electrical design flaw, a bad component, or an incorrectly wired board.
However, several techniques have been evolved for verifying the correctness of the wiring of wrapped wire boards, all of which, nevertheless, suffer from one or more deficiencies. The most obvious and reliable technique for testing the wired boards would be to verify that each pin is electrically connected to the pin(s) that it is supposed to be connected to, and is not electrically connected to all the other pins. For this test may be utilized a simple continuity tester which comprises a meter having two probes which are placed on the two pins whose continuity is to be tested. The meter will indicate whether a short or open circuit exists between the two pins. While extremely reliable, the process of considering each pin in order and testing it with all remaining pins is extremely tedious and time-consuming. In this technique, the number of tests required is (T.sup.2 - T)/2, where T is the total number of pins. The impracticality of this technique becomes clear when one considers that for a relatively small wrapped wire board having one thousand pins, the technique would require 499,500 tests.
An abbreviated and alternative prior art technique simply requires that each branch, which may consist of either two or a plurality of pins, be tested for continuity by placing the probes on the first and last pins of the branch. This technique requires the wiring to be initially accomplished in a sequential or "chain" order, which is both an efficient and acceptable wiring procedure. This method is commonly referred to in the art as "buzzing out" a board, but is not a complete check since it fails to account for any short circuits that may inadvertently occur between branches. Further the technique does not test for the inadvertent wiring of extra wires to pins which were not to be wired at all.
It may therefore be appreciated that the prior art techniques for testing the wiring of wrapped wire electronic circuit boards suffer from complexity, high cost, incomplete testing, or long set-up times. There is therefore a great need for a simplified technique to accomplish such testing.